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UNIVERSITY  OF  ILLINOIS 

Agricultural  Experiment  Station 


BULLETIN  No.  228 


AN  EPIDEMIC  OF  ROPY  MILK 

BY  H.  A.  HARDING  AND  M.  J.  PRUCHA 


URBANA,  ILLINOIS,  JUNE,  1920 


SUMMARY  OF  BULLETIN  No.  228 

Ropy  milk  is  due  to  the  growth  in  the  milk  of  certain  germs,  and  this 
growth  results  in  an  increased  viscosity  of  the  milk.  There  is  no  evidence  that 
these  germs  produce  any  changes  which  affect  either  the  healthfulness  or  the 
flavor  of  the  milk,  but  the  change  in  consistency  is  unusual  and  on  this  account 
is  objectionable  to  the  consuming  public. 

The  source  from  which  an  outbreak  of  ropy  milk  actually  starts  has  not 
been  accurately  determined.  In  practically  all  outbreaks  in  connection  with 
large  milk  companies  the  trouble  appears  first  in  the  milk  furnished  by  one  or 
two 'farms.  This  would  suggest  that  the  trouble  starts  at  the  farm  rather  than 
at  the  plant.  At  such  farms  the  germs  causing  the  trouble  can  usually  be  found 
both  in  the  utensils  and  in  the  cooling  tanks.  It  is  frequently  reasoned  that  the 
cooling  tanks  have  been  infected  from  the  utensils,  but  the  observed  facts  sug- 
gest that  the  utensils  may  have  been  infected  from  the  water  in  the  cooling  tank. 
Altho  one  of  the  most  common  of  the  ropy  milk  germs  was  originally  isolated 
from  water  which  was  not  known  to  be  in  any  way  connected  with  milk,  there 
is  little  known  regarding  the  distribution  of  ropy  milk  germs  in  water  supplies. 
In  the  cases  here  reported,  in  which  the  ropy  milk  germs  were  recovered  from 
the  coat  of  the  cow,  the  recent  infection  of  the  coat  by  infected  water  was 
also  noted. 

A  thoro  application  of  a  disinfecting  solution  to  the  cooling  tank,  the  uten- 
sils, and  the  milk  house  usually  results  in  the  disappearance  of  the  trouble  at 
the  farm,  tho  in  some  cases  it  may  be  desirable  to  extend  the  treatment  to  the 
coat  of  the  cows  and  to  the  stables. 

The  outbreak  here  described  was  unusual  in  that  it  took  on  the  character- 
istics of  an  epidemic  involving  practically  an  entire  dairy  community. 

While  the  production  of  a  satisfactory  milk  from  a  supply  heavily  infected 
with  ropy  milk  germs  presents  some  practical  difficulties,  it  is  not  impossible. 
None  of  the  germs  causing  ropy  milk,  which  have  thus  far  been  studied,  are 
able  to  withstand  a  heating  to  140°  F.  for  thirty  minutes.  Accordingly,  if  the 
milk  is  properly  pasteurized  for  this  time  and  at  this  temperature  and  is  pro- 
tected from  reinfection  with  the  germs  of  ropy  milk,  it  will  be  satisfactory  to 
the  trade.  This  result  may  be  accomplished  under  commercial  conditions  by 
giving  careful  attention  to  the  details  of  pasteurization  and  by  daily  treating 
all  parts  of  the  milk-handling  machinery  with  flowing  steam. 


AN  EPIDEMIC  OF  ROPY  MILK 

BY  H.  A.  HARDING,  CHIEF  IN  DAIRY  BACTERIOLOGY,  AND 
M.  J.  PEUCHA,  ASSOCIATE  CHIEF  IN  DAIRY  BACTERIOLOGY 

INTRODUCTION 

Outbreaks  of  ropy  milk  involving  a  single  or  a  few  farms  occur 
frequently,  but  during  the  past  season  the  attention  of  the  authors 
was  drawn  to  a  severe  outbreak  involving  more  than  one  hundred 
farms  and  presenting  the  general  picture  of  an  epidemic.  As  both 
the  germ  causing  the  trouble  and  the  epidemic  nature  of  the  outbreak 
were  somewhat  unusual,  it  seems  desirable  to  bring  the  known  facts 
to  the  attention  of  the  dairy  industry. 

In  presenting  the  details  of  this  epidemic  of  ropy  milk  the  authors 
have  drawn  freely  upon  the  observations  and  experience  of  men  in 
the  milk  industry  and  particularly  upon  certain  of  these  men  who  are 
well  trained  in  dairy  bacteriology.  It  would  be  a  pleasure  to  make 
more  detailed  and  specific  acknowledgement  of  these  contributions 
were  it  not  for  the  expressed  wish  of  the  commercial  firms  involved 
that  no  mention  of  their  companies  or  their  men  appear  in  the  pub- 
lication. 

WHAT  IS  KOPY  MILK 

The  term  ropy  or  slimy  is  applied  to  milk  which  has  become 
noticeably  more  viscous  than  ordinary  milk.  When  this  ropiness  is 
only  slightly  developed  it  is  ordinarily  overlooked.  It  is  sometimes 
noticed  from  the  fact  that  the  milk  pours  more  slowly  or  because  the 
last  portion  drips  from  the  container  with  the  formation  of -an  evident 
thread  of  milk. 

Where  the  viscosity  is  more  pronounced,  the  milk  may  be  drawn 
out  by  means  of  a  fork,  or  similar  object,  into  threads.  In  extreme 
cases  these  threads  may  be  fine  and  silky  and  more  than  a  foot  long, 
tho  more  frequently  they  break  when  only  an  inch  or  less  in  length. 

In  extreme  cases  the  milk  takes  on  almost  the  consistency  of  a 
sticky,  stiff  dough,  and  a  cup  of  it  may  be  inverted  without  the  milk 
being  spilled. 

Eopy  milk  should  not  be  confused  with  the  results  of  garget. 
Garget  is  an  inflamed  condition  of  the  udder  of  the  cow,  and  milk 
as  it  comes  from  such  inflamed  udders  frequently  contains  white 
masses  or  strings  of  coagulated  material.  Milk  which  becomes  ropy, 
on  the  other  hand,  comes  from  healthy  udders  and  is  normal  when 
drawn,  but  the  ropiness  may  appear  at  any  time  after  twelve  hours. 

Ill 


112  BULLETIN  No.  228  [June, 

WHAT  CAUSES  ROPY  MILK 

There  are  at  least  three  common  and  distinct  types  of  ropy  milk : 

(1)  the  ropiness  produced  in  milk  drinks  by  the  Bulgarian  bacillus; 

(2)  the  ropiness  in  starter  for  butter-making,  resulting  from  the 
degeneration  of  the  starter  culture;  and  (3)  the  ropiness  which  ap- 
pears in  sweet  milk. 

In  the  preparation  of  buttermilk  for  the  city  trade  difficulties 
arise  from  the  tendency  of  the  solids  of  the  buttermilk  to  settle  to 
the  bottom,  leaving  the  thin  whey  on  top.  In  order  to  check,  if 
not  entirely  prevent  this  settling,  it  is  customary  to  add  to  the  butter- 
milk a  viscous  culture  of  bulgaricus — "the  bacillus  of  long  life." 
This  organism  not  only  gives  an  attractive  acid  flavor  to  the  butter- 
milk, but  also  makes  it  quite  viscous  and  gives  it  a  pleasing  smoothness 
to  the  tongue. 

Again  in  the  propagation  of  an  entirely  different  type  of  acid- 
producing  bacteria  in  connection  with  the  ripening  of  cream  for 
butter-making,  it  not  infrequently  happens  that  on  continued  cultiva- 
tion these  cultures  take  on  the  habit  of  making  the  ripening  cream 
quite  viscous.  This  change  is  generally  considered  undesirable  in 
the  making  of  butter,  and  such  cultures  are  accordingly  rejected. 

It  should  be  noted  that  from  the  standpoint  of  business  one  of 
the  above  types  of  ropiness  is  useful  and  is  accordingly  encouraged, 
and  the  other  is  undesirable  and  is  discarded,  and  that  both  types 
of  ropiness  appear  in  sour  milk  or  cream.  The  viscosity  in  the  sour 
milk  or  cream  develops  uniformly  thruout  the  entire  mass  or  even 
better  toward  the  bottom  of  the  container,  and  it  develops  most 
rapidly  at  relatively  high  temperatures.  The  best  growth  of  the 
bulgaricus  organisms  occurs  at  or  above  blood  heat. 

The  ropiness  with  which  this  publication  is  primarily  concerned 
makes  trouble  in  connection  with  city  milk.  It  appears  in  sweet, 
well-cared  for  milk,  and  ordinarily  as  soon  as  the  milk  begins  to 
sour  the  viscosity  disappears.  Moreover,  this  ropiness  in  sweet  milk 
develops  most  markedly  at  the  surface  in  contact  with  the  air,  and 
rarely  appears  unless  the  milk  is  kept  relatively  cold.  When  the 
milk  is  held  at  higher  temperatures,  acid  develops  and  destroys  the 
viscosity. 

Because  of  the  outstanding  differences  between  the  development 
of  viscosity  in  the  sour  and  in  the  sweet  milk  it  is  clear  that  the 
viscosity  in  the  two  cases  must  arise  from  distinctly  different  causes. 

Since  the  ropiness  is  not  present  in  the  milk  as  drawn,  but  de- 
velops when  the  milk  is  one  or  two  days  old,  it  seems  plain  that  it 
must  be  due  to  something  which  grows  in  the  milk.  Studies  of  the 
germ  life  in  such  milk  have  shown  the  presence  of  germs  which  are 
the  cause  of  the  ropiness.  These  germs  can  be  separated  from  the 
milk,  can  be  cultivated  in  the  laboratory  on  gelatin  and  other  sub- 


1920}  AN  EPIDEMIC  OF  EOPY  MILK  113 

stances  for  months,  and  when  returned  to  samples  of  sterile  milk 
will  reproduce  the  ropiness  in  the  usual  way. 

For  nearly  a  hundred  years  outbreaks  of  ropy  milk  have  been 
reported  occasionally,  and  a  number  of  different  germs  have  been 
found  which  are  able  to  bring  about  this  change  in  the  milk. 

WHY  IS  EOPY  MILK  OBJECTIONABLE 

With  milk,  as  with  other  foods,  custom  is  a  large  factor  in  es- 
tablishing market  demands.  There  is  no  question  but  that  our  retail 
milk  trade  calls  for  a  sweet  milk  of  normal  consistency  and  taste. 
While  the  growth  of  the  ropy  milk  germs  ordinarily  produces  little 
change  in  the  taste  of  the  milk,  these  organisms  do  change  its  con- 
sistency so  noticeably  as  to  arouse  the  suspicions  of  the  consumer. 

The  agitation  of  recent  years  for  milk  of  low  germ  content  has 
made  the  consumer  very  suspicious  of  any  evidence  of  germ  growth 
in  milk  and  doubly  so  of  unusual  appearances. 

While  there  is  no  evidence  nor  any  reason  to  believe  that  the 
growth  of  the  ropy  milk  organism  is  in  any  way  harmful  to  the  con- 
sumer, such  milk  is  not  acceptable  to  the  American  consuming  public, 
and  accordingly  is  neither  profitable  nor  desirable  in  the  city  milk 
supply. 

WHY  IS  ROPY  MILK  SO  COMMON  A  TROUBLE 

It  should  be  remembered  that  the  germs  of  ropy  milk  which  ordi- 
narily make  trouble  in  connection  with  the  city  supply  do  not  thrive 
in  connection  with  the  ordinary  acid-producing  germs.  When  milk 
is  produced  with  a  lack  of  care  as  to  the  utensils  and  is  handled  with- 
out proper  regard  to  cooling,  the  rapid  development  of  the  acid-pro- 
ducing germs  interferes  with  the  activity  of  the  ropy  milk  organisms 
even  if  present. 

Before  the  cause  of  ropy  milk  was  clearly  understood,  a  treatment 
often  recommended  was  to  rinse  all  utensils  with  sour  milk  and  allow 
them  to  stand  some  hours  before  washing.  In  this  case  the  remedy 
was  worse  than  the  trouble  it  aimed  to  cure  because  it  resulted  in 
the  quick  souring  of  the  milk,  but  it  was  efficient  in  checking  the 
development  of  the  ropiness.  The  germs  producing  ropy  milk  thrive 
at  a  temperature  much  below  that  most  favorable  for  the  growth  of 
the  ordinary  acid-producing  germs.  Accordingly,  when  the  ropy 
milk  germs  are  present,  cooling  of  the  milk  checks  them  but  little  and 
in  such  cooled  milk  they  have  an  advantage  over  the  acid  producers. 

It  is  a  matter  of  common  knowledge  that  during  the  warm  summer 
weather  the  acid-producing  germs  develop  quickly  in  the  milk  and 
unless  considerable  care  is  exercised  the  milk  does  not  remain  sweet 
for  twenty-four  hours.  On  the  other  hand,  in  the  winter  the  low 


114  BULLETIN  No.  228  [June, 

temperatures  are  favorable  to  the  development  in  the  milk  of  quite 
a  different  class  of  germ  life,  with  the  result  that  if  the  milk  is  kept 
cold  it  will  frequently  remain  sweet  for  two  weeks  and  even  then 
will  not  become  sour  but  will  undergo  other  undesirable  changes. 

In  the  spring  when  winter  is  changing  to  summer  conditions,  and 
again  in  the  fall  when  the  reverse  change  takes  place,  the  germ  life 
in  the  milk  is  quite  variable.  At  these  times  of  the  year  a  majority 
of  the  outbreaks  of  ropy  milk  appear.  In  case  an  outbreak  at  such 
a  time  becomes  well  established  it  may  persist  for  some  weeks  or 
months. 

AT  WHAT  POINT  DO  ROPY  MILK  GERMS  GET 
INTO  THE  MILK 

Knowing  that  ropiness  in  milk  is  due  to  the  growth  in  it  of  cer- 
tain germs,  the  first  step  is  to  locate  the  sources  from  which  such 
germs  enter  the  milk.  Where  time  permits  and  where  some  thoroly 
boiled  or  steamed  bottles  are  at  hand,  the  point  at  which  the  ropy 
milk  germs  enter  the  milk  may  be  readily  determined  by  collecting 
and  observing  samples  of  the  milk.  These  samples  may  be  taken 
by  milking  from  each  cow  directly  into  bottles,  and  by  collecting 
samples  of  milk  at  the  emptying  of  each  pail  as  the  milk  flows  from 
the  strainer,  and  by  pouring  from  each  can.  Hair,  dust,  and  dand- 
ruff from  the  coat  of  each  cow,  and  water  from  the  cooling  tank 
should  likewise  be  collected  and  freshly  boiled  milk  added  so  that 
any  ropy  germs  present  may  have  a  chance  to  show  themselves. 
Samples  collected  in  this  way  are  best  stoppered  with  cotton  to  pre- 
vent further  contamination  and  to  provide  an  abundant  supply  of 
air  to  the  surface  of  the  milk.  These  milk  samples  should  also  be 
kept  fairly  cool  since  high  temperatures  will  favor  the  growth  of 
the  acid-forming  germs  which  may  overgrow  the  ropy  ones. 

Naturally  suspicion  was  early  directed  to  the  udder  of  the  cow 
as  a  possible  source  of  ropy  milk  germs.  While  it  is  a  fact  that  the 
milk  as  it  comes  from  the  udder  of  the  cow  ordinarily  contains  about 
500  bacteria  per  cubic  centimeter  (about  20  drops),  the  past  studies 
of  the  germ  content  of  normal  udders  and  the  studies  of  the  sources 
of  the  outbreaks  of  ropy  milk  have  uniformly  failed  to  show  that 
the  germs  coming  from  the  udder  are  ever  the  cause  of  ropy  milk. 

During  the  act  of  milking  some  foreign  matter  falls  into  the  milk 
and  there  is  always  the  possibility  that  this  material  will  carry  on 
it  the  germs  which  produce  ropy  milk.  It  has  been  repeatedly  shown 
that  the  germs  causing  ropy  milk  live  in  water,  and  when  cows  wade 
in  infected  water  there  is  always  the  possibility  of  their  getting  the 
germs  upon  their  coats.  Observations  have  been  made  by  different 
investigators  to  determine  whether  these  germs  have  been  actually 


1920}  AN  EPIDEMIC  OF  KOPY  MILK  115 

introduced  into  the  milk  from  the  coat  of  the  cow.  In  a  few  instances, 
and  two  of  these  were  in  connection  with  the  present  outbreak,  there 
is  strong  evidence  that  this  may  have  occurred.  On  the  other  hand, 
it  is  the  usual  experience  that  when  attention  is  given  to  certain 
other  possible  factors  the  trouble  immediately  stops  without  any  at- 
tention being  paid  to  the  coat  of  the  cow.  Such  results  would  suggest 
that  only  in  rare  cases  is  the  coat  of  the  cow  a  source  from  which 
ropy  milk  organisms  are  brought  into  the  milk. 

Samples  taken  in  the  manner  above  described,  in  connection  with 
many  different  outbreaks  on  farms,  have  ordinarily  shown  that  the 
utensils  are  the  source  from  which  the  ropy  germs  enter  the  milk. 
Since  the  utensils  on  the  farm  are  commonly  all  washed  together  it 
is  to  be  expected,  and  it  is  common  experience,  that  where  one  is 
infected,  the  ropy  germs  are  present  on  many  or  all  of  the  utensils. 
It  should  be  noted  in  this  connection  that  in  an  outbreak  studied  by 
one  of  the  authors  (H)  in  New  York,  the  ropy  germs  were  found  only 
in  the  cans,  and  the  indications  were  that  in  this  outbreak  the  cans 
were  being  contaminated  while  being  washed  at  the  milk  plant. 

The  source  from  which  the  first  utensil  became  contaminated  in 
the  outbreaks  which  have  been  studied  has  not  been  made  clear.  The 
germ  which  has  been  most  commonly  found  in  ropy  milk  was  orig- 
inally found  in  water,  and  in  outbreaks  on  the  farm  it  is  often  found 
in  the  water  in  the  cooling  tanks.  As  in  such  outbreaks  the  germs 
are  also  found  on  the  utensils  it  is  customary  to  explain  the  presence 
of  the  germ  in  the  cooling  tank  as  resulting  from  the  infected  cans 
having  been  put  in  the  tank.  Where  no  definite  information  is  at 
hand  to  explain  how  the  utensils  became  infected  it  is  quite  as  logical 
to  assume  that  they  became  infected  from  the  water.  Ground  water 
always  carries  a  fair  amount  of  germ  life  of  kinds  best  fitted  to  thrive 
under  such  conditions.  However,  the  studies  which  have  been  made 
of  the  germ  life  of  ground  water  have  not  shown  the  ropy  milk 
organism  to  be  one  of  the  forms  common  in  water.  On  the  other 
hand,  the  knowledge  of  the  germ  life  of  ground  water  is  not  suffi- 
ciently complete  to  show  that  this  germ  is  not  one  of  the  less  common 
water  forms.  The  assumption  that  it  is  a  form  occurring  occasionally 
in  water  and  that  it  occasionally  finds  its  way  into  milk  is  supported 
by  many  of  the  known  facts.  Such  an  assumption  also  serves  to  ex- 
plain the  wide  distribution  of  this  trouble  as  well  as  its  occasional 
appearance  without  any  known  connection  with  any  previous  outbreak. 

ORDINARY  TREATMENT  ON  FARMS 

While  studies  as  outlined  above  will  give  accurate  information  as 
to  the  point  at  which  the  germs  are  entering  the  milk  supply  in  any 
particular  outbreak  and  will  indicate  how  this  infection  can  be  cut 


116  BULLETIN  No.  228  [June, 

off  with  greatest  certainty  and  least  expense,  the  dairymen  are  usually 
most  interested  in  promptly  removing  the  source  of  infection,  even 
if  this  summary  treatment  involves  perhaps  a  little  unnecessary  work. 

Under  ordinary  conditions  the  trouble  is  most  effectively  attacked 
by  emptying  the  cooling  tank,  scrubbing  it  and  filling  it  with  clean 
water  to  which  some  active  disinfectant  is  added.  A  twelve-ounce 
can  of  good  strength  bleaching  powder  (chlorinated  lime)  added  to 
a  100-gallon  tank  will  give  a  powerful  disinfecting  solution.  In  case 
the  tank  has  a  capacity  of  more  than  200-gallons,  additional  bleaching 
powder  should  be  added. 

All  pails,  strainers,  stirrers,  cloths,  brushes,  and  other  utensils 
which  come  into  contact  with  the  milk  are  then  put  into  this  solution 
and  allowed  to  remain  fifteen  to  twenty  minutes.  The  tank  and  floor 
of  the  milk  house  are  then  scrubbed  with  the  disinfecting  solution. 
Where  facilities  are  at  hand,  the  interior  of  the  milk  house  may  be 
whitewashed,  or  it  may  be  drenched  with  the  solution  from  the  tank. 

Where  a  cooling  tank  is  not  used,  but  a  large  iron  kettle  or  food 
cooker  is  available,  the  same  result  may  be  attained  by  filling  this 
with  boiling  water  and  giving  all  cloths,  brushes,  and  utensils  a 
thoro  treatment  with  hot  water. 

Where  the  dairy  is  located  near  a  canning  factory,  all  these  uten- 
sils may  be  placed  in  a  large  steam  kettle  and  an  exposure  to  the 
influence  of  steam  under  pressure  will  promptly  destroy  the  ropy 
milk  germs. 

Bottling  plants  are  often  provided  with  steam  chambers  in  which 
these  dairy  utensils  may  be  quickly  and  thoroly  treated. 

Bringing  all  parts  of  these  utensils  to  the  temperature  of  boiling 
water,  or  exposing  them  to  the  action  of  a  strong  disinfectant  for  a 
few  minutes,  will  kill  all  germs  of  ropy  milk.  Accordingly  a  single 
treatment  of  the  cooling  tank  and  the  utensils  usually  puts  an  end 
to  an  outbreak  on  a  farm. 

It  should  be  understood  that  this  exposure  to  heat  or  to  disin- 
fectants followed  by  thoro  washing  leaves  nothing  on  the  utensils 
which  will  prevent  the  growth  of  ropy  milk  organisms  if  they  find 
their  way  to  the  utensils  after  treatment.  In  actually  carrying  out 
such  a  disinfecting  campaign  at  the  farm  it  occasionally  happens  that 
some  pail,  dipper,  or  other  object  which  has  been  in  contact  with 
the  ropy  milk,  is  overlooked.  If  in  connection  with  the  handling  of 
the  milk  the  germs  on  this  one  utensil  spread  to  the  others,  the  result 
of  the  disinfection  is  lost  and  the  trouble  will  reappear  in  the  milk. 
Fortunately  in  the  actual  handling  of  outbreaks  the  trouble  rarely 
reappears  where  the  work  is  carefully  done.  This  latter  fact  is  per- 
haps the  strongest  bit  of  evidence  against  the  theory  of  the  natural 
water  supply  being  the  starting  point  of  the  outbreak. 


AN  EPIDEMIC  OF  ROPY  MILK  117 

THE  EPIDEMIC 

About  the  middle  of  June,  1919,  complaints  of  ropy  milk  from 
customers  of  a  large  dairy  company  led  to  observations  at  the  bottling 
plant  handling  this  portion  of  its  supply.  Ropy  milk  is  not  an  un- 
common experience  in  connection  with  the  city  milk  trade,  and  when 
it  appears  a  prompt  study  of  the  source  of  supply  usually  shows  that 
milk  infected  with  ropy  organisms  is  being  furnished  by  one  or  two 
farms.  The  treatment  of  the  utensils  and  cooling  tanks  at  these 
farms  as  already  outlined  quite  regularly  results  in  the  disappearance 
of  the  trouble.  Since  more  or  less  of  this  trouble  appears  every  season 
its  treatment  has  become  practically  a  routine  matter. 

In  the  present  instance  samples  from  each  patron's  milk  were 
collected  in  well-steamed  bottles  as  the  cans  were  being  emptied,  and 
these  bottles,  capped  or  stoppered  with  cotton,  were  held  at  low  tem- 
perature and  observed  for  the  development  of  ropiness. 

Unless  the  infection  is  fairly  heavy  the  ropiness  will  not  be  evident 
before  twenty-four  hours  and  may  not  appear  before  forty-eight 
hours.  Where  the  germs  are  fairly  abundant,  the  entire  upper  sur- 
face of  the  cream  becomes  noticeably  viscous.  Examinations  are  best 
made  with  a  small  bent  platinum  wire  which  is  heated  to  redness  and 
cooled  before  the  examination  of  each  bottle  so  as  to  prevent  the 
transfer  of  germs  from  one  bottle  to  the  next.  When  this  wire  is 
thrust  below  the  surface  of  the  cream  and  is  withdrawn,  the  viscous 
milk  is  drawn  out  into  a  thread,  the  length  and  thickness  of  which 
varies  with  the  degree  of  ropiness.  In  making  such  examinations  of 
milk  in  bottles  which  have  been  stoppered  with  cotton,  care  should 
be  exercised  not  to  be  misled  by  the  presence  in  the  milk  of  cotton 
fibers.  When  such  a  fiber  is  caught  by  the  wire  it  often  closely  re- 
sembles a  thread  of  ropy  milk.  Where  such  a  wire  is  lacking,  wooden 
toothpicks  or  forks  may  be  used.  However,  unless  a  fresh  one  is 
used  for  each  bottle,  examinations  on  succeeding  days  may  lead  to 
wrong  conclusions  because  of  the  transfer  of  germs  from  one  bottle 
to  another. 

Where  the  infection  is  not  abundant,  the  ropiness  of  the  cream 
may  be  confined  to  small  islands  or  even  to  very  small  points  on  the 
surface.  At  these  points  there  is  evidently  the  development  of  colonies 
of  the  germs  causing  the  trouble.  The  experienced  observer  can  often 
locate  these  points  of  ropiness  by  observing  the  presence  of  what  ap- 
pear to  be  small  drops  of  fat  in  the  cream.  In  many  cases  the  milk 
surrounding  these  drops  of  fat  is  very  ropy.  On  the  other  hand,  in 
an  occasional  bottle  these  drops  are  evident  and  the  milk  is  not  ropy, 
while  in  many  cases  the  milk  is  ropy  without  the  presence  of  these 
drops  of  fat.  While  the  relation  of  these  drops  of  fat  to  the  germs 
causing  the  trouble  is  not  entirely  clear,  the  connection  between  these 


118  BULLETIN  No.  228  [June, 

drops  and  the  ropiness  is  too  regular  to  be  a  mere  accident. 

Samples  were  taken  and  examined  in  this  way  from  the  milk  of 
each  of  the  140  patrons  bringing  milk  to  the  bottling  plant  in  ques- 
tion, and  ropiness  was  noted  one  or  more  times  in  samples  from  116 
of  these  farms.  Late  in  the  season  when  a  neighboring  cheese  factory 
closed  and  a  number  of  its  patrons  transferred  their  product  to  the 
bottling  plant,  they  also  were  found  to  be  bringing  the  ropy  organisms. 
Inquiries  in  the  community  in  a  few  cases  where  a  cow  was  kept  by 
a  family  that  was  not  otherwise  connected  with  the  dairy  business 
showed  that  here  too  trouble  was  being  experienced  with  ropy  milk. 
In  short  it  appeared  that  here  was  a  community-wide  epidemic  of 
ropy  milk  which  not  only  included  the  larger  part  of  the  patrons  of 
the  bottling  plant,  but  also  included  people  not  directly  connected 
with  the  milk  shipping  industry. 

OBSERVATIONS  ON  THE  FARMS 

The  finding  of  ropy  milk  organisms  in  the  milk  as  delivered  at 
the  bottling  plant  was  followed  by  a  collection  of  samples  at  the  farms. 

These  samples  ordinarily  showed  the  presence  of  the  ropy  organ- 
isms in  the  utensils  and  in  many  cases  also  showed  their  presence 
in  the  water  in  the  cooling  tank. 

The  observations  made  at  one  farm  are  sufficiently  important  to 
deserve  special  mention.  At  this  farm  the  germs  were  repeatedly 
shown  to  be  present  on  the  utensils  and  in  the  water  of  the  cooling 
tank.  From  the  cooling  tank  the  water  flowed  to  the  stock  watering 
tank  located  in  the  barn  yard,  and  the  presence  of  the  ropy  milk 
germs  was  repeatedly  demonstrated  in  the  water  from  the  stock  tank. 

The  stock  tank  overflowed  and  leaked  into  the  barn  yard,  forming 
considerable  mud  thru  which  the  cows  came  to  drink. 

In  drinking  the  cows  rubbed  against  the  wet  sides  of  the  tank 
and  their  coats  also  became  moistened  by  the  noses  of  their  com- 
panions. Some  mud  also  got  upon  their  coats. 

On  two  different  occasions  material  collected  from  the  flank  and 
udder  of  these  cows  and  put  into  sterile  milk  produced  characteristic 
ropiness,  indicating  the  presence  of  the  ropy  milk  germs.  Both  of 
these  tests  were  made  by  the  bacteriologist  of  the  milk  company.  At 
one  of  the  tests  one  of  the  authors  (H)  was  present  and  observed  the 
conditions  of  the  barn  yard  and  the  details  of  the  test,  and  he  sees 
no  reason  to  doubt  that  under  these  conditions  the  ropy  germs  were 
present  on  the  coat  of  the  cow  and  from  it  could  have  been  trans- 
ferred to  the  milk. 

TREATMENT  OF  THE  CANS  AT  THE  BOTTLING  PLANT 

At  the  bottling  plant  the  cans,  after  being  emptied,  were  well 
washed  by  a  revolving  brush  machine.  They  were  then  passed  sue- 


1920]  AN  EPIDEMIC  OF  EOPY  MILK  119 

cessively  over  two  steam  jets  and  two  air  blasts.  The  can  covers  were 
also  given  a  similar  treatment  with  steam  and  air. 

When  careful  attention, was  given  to  the  steaming,  the  cans  were 
undoubtedly  heated  sufficiently  to  very  materially  reduce  the  number, 
it  not  totally  destroy,  any  ropy  milk  germs  in  them.  On  the  other 
hand,  it  is  very  doubtful  whether  as  much  could  be  said  of  the  treat- 
ment of  the  can  covers.  The  covers  are  much  more  difficult  to  steam 
properly  and  even  more  difficult  to  dry  over  the  air  blast.  It  is 
rare  indeed  that  the  present  available  can-drying  machinery  delivers 
a  dry  can,  and  the  result  is  that  the  moist  cans  as  usually  returned 
to  the  farms,  permit  a  marked  development  in  them  of  such  germ 
life  as  survives  the  steaming  process. 

At  the  beginning  of  the  outbreak  the  washing  of  all  the  cans  at 
the  bottling  plant  in  a  single  vat  probably  offered  a  chance  of  passing 
the  germs  of  ropy  milk  from  the  cans  of  one  farm  to  those  of  another. 
All  that  then  prevented  the  extension  of  the  trouble  to  other  farms 
was  the  action  of  the  steam  jet  and,  as  has  just  been  pointed  out, 
the  steaming  and  drying  process  was  hardly  equal  to  killing  all  of 
the  germ  life  in  the  cans. 

As  soon  as  the  seriousness  of  the  situation  was  realized  the  treat- 
ment of  the  washed  cans  by  steam  was  followed  by  the  immersing  of 
the  cans  and  their  covers  in  a  tank  containing  a  strong  solution  of 
bleaching  powder.  After  this  practice  was  adopted  there  is  little 
probability  that  the  mingling  of  the  cans  at  the  bottling  plant  was 
longer  a  factor  in  spreading  the  trouble  among  the  dairies. 

DISINFECTION  AT  THE  FARMS 

The  disinfection  of  the  cooling  tanks  and  utensils  at  the  farms 
which  were  bringing  ropy  milk  to  the  bottling  plant  was  carried  out 
in  the  routine  manner,  bleaching  powder  being  used  as  a  disinfectant. 
Later,  in  addition,  the  interior  of  the  milk  house  and  the  cow  stable 
was  thoroly  sprayed  with  whitewash  containing  bleaching  powder. 
In  a  considerable  number  of  instances  the  coat  and  udder  of  the  cows 
were  also  moistened  with  the  bleaching  powder  solution. 

While  this  treatment  ordinarily  resulted  in  the  disappearance  of 
the  ropy  milk  germs  from  the  milk  produced  at  such  farms,  occas- 
ionally the  trouble  reappeared.  Particularly  was  this  true  in  the 
earlier  part  of  the  epidemic  when  the  trouble  was  most  abundant 
and  when  facilities  for  thoro  treatment  were  not  so  well  developed. 

As  this  treatment  progressed,  the  amount  of  ropy  milk  coming  to 
the  bottling  plant  decreased,  but  as  it  is  the  nature  of  an  epidemic 
to  die  out,  this  decrease  cannot  be  attributed  with  entire  certainty 
to  the  treatment. 


120 


BULLETIN  No.  228 
OBSERVATIONS  AT  THE  BOTTLING  PLANT 


[June, 


Since  the  arrangement  of  machinery  differs  considerably  in  various 
milk  plants,  a  discussion  of  the  problem  presented  by  this  particular 
plant  and  its  treatment  will  be  made  clearer  by  reference  to  the  ac- 
companying floor  plan. 


1  Weigh  Tank  7  Heating  Coils 

2  Eeceiving  Tank  8  Holding    Section 

3,  6,  16  Milk  Pumps  9  Cooling  Coils 

4,  5  Clarifier  and  Tank  10  Storage  Tank 


11,  12  Fillers   and   Cappers 
1.3  Separator  and  Cream  Cooler 

14  Can  Einse 

15  Can  Washer  and  Sterilizer 


The  room  in  which  the  incoming  milk  is  weighed  and  the  cans 
washed  and  returned  to  the  patrons  is  ten  feet  above  the  floor  of 
the  milk-handling  room.  Accordingly  the  milk  flows  by  gravity  from 
the  weighing  can  to  the  receiving  tank  and  from  this  is  pumped  to 
the  clarifier.  The  clarifier  discharges  into  a  small  tank  from  which 


L9%0]  AN  EPIDEMIC  OF  EOPY  MILK  121 

a  pump  drives  the  milk  thru  a  tubular  heater  and  a  tubular  holder. 
This  milk  holder  discharges  into  a  small  tank  from  which  a  second 
pump  forces  the  milk  thru  a  tubular  cooler  and  into  an  elevated 
storage  tank.  From  this  storage  tank  the  milk  flows  by  gravity  to 
two  rotary  bottlers  and  thence  into  the  bottles.  All  necessary  con- 
nections are  with  so-called  "sanitary  pipe"  and  fittings  which  can 
be  taken  down  for  cleaning. 

While  this  floor  arrangement  provides  ample  working  space  it 
should  be  noted  that  the  receiving  tank,  in  which  the  untreated  milk 
from  the  farms  is  being  collected,  is  only  about  twenty  feet  from  the 
point  where  the  milk  is  being  bottled.  While  there  is  no  evident 
direct  connection  between  these  points  except  thru  the  pasteurizer, 
the  presence  and  activities  of  six  or  more  workmen,  each  intent  on 
completing  the  work  of  the  day,  offers  some  chance  of  cross  infection. 

MILK-HANDLING  PROBLEM  AT  THE  BOTTLING  PLANT 

With  a  considerable  proportion  of  the  patrons  bringing  milk  well 
seeded  with  ropy  milk  germs,  the  problem  of  supplying  satisfactory 
city  milk  was  a  difficult  one  for  the  bottling  plant. 

The  available  method  of  solving  this  problem  was  to  thoroly 
pasteurize  all  the  milk  and  then  to  protect  the  pasteurized  milk  so 
carefully  that  no  more  of  the  ropy  milk  germs  could  get  into  it.  The 
thoro  pasteurization  and  the  complete  after-protection  each  presented 
difficulties  which  are  not  always  appreciated. 

Careful  laboratory  studies  of  the  ropy  milk  germs  from  this  and 
from  a  number  of  other  outbreaks  showed  that  when  milk  containing 
a  heavy  inoculation  of  such  germs  was  held  at  140°  F.,  a  number  of 
the  ropy  milk  germs  were  alive  at  the  end  of  10  minutes,  a  few  (in- 
cluding the  germ  from  this  epidemic)  were  alive  at  the  end  of  20 
minutes,  but  all  of  them  were  dead  at  the  end  of  30  minutes.  Accord- 
ingly, if  the  pasteurizing  process  is  to  totally  destroy  the  germs  of 
ropy  milk,  it  is  necessary  that  every  particle  of  the  milk  shall  be 
held  at  or  above  140°  F.  for  30  minutes. 

The  details  of  pasteurization  vary  considerably  with  the  different 
types  of  machines.  However,  with  most  types  of  pasteurizers  it  re- 
quires careful  management  to  ensure  that  the  first  milk  thru  the  ma- 
chine is  heated  neither  too  much  nor  too  little.  If  heated  too  much 
the  milk  tends  to  lose  its  cream  line  and  may  acquire  a  cooked  taste. 
Knowing  this,  the  operator  of  the  pasteurizer  is  prone  to  err,  if  at  all, 
on  the  side  of  too  low  rather  than  too  high  heating  of  the  first  milk. 
From  the  time  the  pasteurizer  is  completely  in  operation  until  the 
close  of  the  process,  there  is  less  difficulty  in  accurately  controlling 
the  temperature,  tho  the  possibility  of  leaky  valves  should  always 
be  considered.  However,  at  the  end  of  the  process  there  is  often 


122  BULLETIN  No.  228  [June, 

difficulty  in  being  sure  that  the  last  milk  thru  the  pasteurizer  has 
received  its  allotted  amount  of  heating.  Accordingly,  unless  the  plant 
foreman  gives  personal  attention  to  these  details,  a  portion  of  the 
first  or  of  the  last  milk  may  slip  past  the  pasteurizer  without  receiv- 
ing a  heating  sufficient  to  destroy  the  ropy  milk  germs.  If  any  of 
them  pass  this  point  alive,  there  is  no  means  available  for  preventing 
their  development  in  the  bottled  milk. 

Even  where  the  pasteurizing  process  is  all  that  could  be  desired, 
as  soon  as  the  milk  is  sufficiently  cool  it  is  liable  to  reinfection.  Ex- 
perience with  utensils  at  the  farm  shows  that  the  germs  of  ropy  milk 
grow  readily  upon  dairy  utensils.  If  in  any  way  these  germs  get 
into  the  piping,  storage  vat,  or  upon  the  cooler,  the  bottlers,  or  other 
utensils,  they  are  able  to  grow  and  they  are  in  a  position  to  reinfect 
even  properly  pasteurized  milk. 

As  a  protection  against  such  reinfection  it  is  not  enough  to  thoroly 
clean  all  piping  and  utensils  —  a  further  thoro  treatment  should 
be  given  them  with  boiling  water,  or  preferably  with  steam.  In  the 
case  of  sanitary  piping  and  small  utensils  this  is  relatively  easy,  pro- 
vided there  is  a  sufficiently  large  steam  chamber  in  which  they  may 
be  treated.  Bringing  all  parts  of  such  utensils  to  200°  F.  even  for 
a  few  seconds  is  sufficient.  In  the  absence  of  such  a  steam  chamber 
a  large  vat  may  be  used.  If  a  fairly  heavy  canvas  (10  ounce)  is 
fastened  snugly  over  such  a  vat  containing  the  utensils,  and  steam 
is  passed  freely  into  the  vat,  the  cover  will  retain  practically  all  of 
the  steam.  If  at  the  close  of  the  treatment  the  canvas  cover  is  re- 
moved and  suspended  while  still  hot,  it  will  usually  dry  promptly. 
A  canvas  cover  may  be  used  in  a  similar  way  to  facilitate  the  steam- 
ing of  the  bottlers,  and  with  slight  modifications  the  horizontal  cool- 
ers may  also  be  steamed.  In  the  case  of  an  unusually  large  cooler 
it  may  be  more  convenient  to  cover  and  steam  the  sections  separately. 

The  steaming  of  horizontal  coolers  should  always  be  undertaken 
carefully.  In  many  cases  pipes  are  not  strongly  held  at  the  ends 
and  if  the  cooler  is  unevenly  heated  the  uneven  expansion  of  the 
metal  may  result  in  leaks. 

In  practice  it  is  difficult  to  bring  about  so  thoro  a  treatment  of 
the  utensils  as  to  include  all  parts  of  the  cream  and  fermented-milk 
divisions,  and  unless  these  are  included  there  is  always  the  chance 
of  a  slight  reinfection.  Perhaps  the  greatest  practical  difficulty  in 
this  connection  is  with  the  steaming  of  milk  pumps.  While  their 
working  parts  may  be  easily  removed  and  steamed,  the  remaining 
portion  of  some  of  the  pumps  cannot  be  readily  steamed  with  these 
parts  removed,  and  when  they  are  in  place  the  valves  prevent  a  flow 
of  steam  and  mechanically  protect  a  portion  of  the  pump.  Likewise, 
the  steam  may  not  enter  the  air  chamber  above  the  pump. 


1920}  AN  EPIDEMIC  OF  EOPY  MILK  123 

Even  where  the  cleaning  process  of  the  day  includes  as  thoro  a 
steaming  as  suggested  above,  it  is  well  to  begin  operations  the  follow- 
ing day  by  flushing  out  the  piping  and  machinery  with  an  abundance 
of  hot  water  or  steam. 

It  is  a  common  practice  to  bottle  cream  before  beginning  to  bottle 
milk.  The  cream  adhering  to  the  bottler  mixes  with  the  milk  and 
slightly  increases  its  fat  content.  While  this  slightly  increases  the 
food  value  of  the  milk  it  also  increases  its  germ  content  and  thereby 
hastens  the  souring  of  the  milk.  In  an  outbreak  of  ropy  milk,  which 
came  under  our  observation  some  years  since,  this  practice  was  the 
means  of  carrying  over  a  culture  of  ropy  milk  germs  and  thus -in- 
fecting the  bottler  which  had  previously  been  carefully  steamed.  As 
a  result  even  where  all  the  milk  handling  machinery  had  been  prop- 
erly treated,  the  milk  supplied  to  the  trade  continued  to  become  ropy 
until  this  infection  of  the  bottler  was  recognized  and  stopped.  In 
this  case  the  cream  cans  became  infected  in  the  common  washing 
vat  and  were  not  sufficiently  steamed  to  free  them  of  the  ropy  organ- 
isms. When  later  filled  with  cream  and  held  in  storage  until  the 
following  morning,  the  ropy  germs  grew  in  cold  storage,  forming  a 
starter  which  heavily  infected  the  bottler.  The  difficulty  would  prob- 
ably have  been  avoided  by  properly  steaming  the  cans  in  which  the 
cream  was  held,  but  as  a  more  certain  precaution  the  bottling  of 
the  cream  was  delayed  until  after  the  bottling  of  the  milk.  Had 
an  earlier  bottling  been  necessary  it  might  have  been  followed  by  a 
washing  and  steaming  of  the  bottler,  which  is  the  present  practice 
in  some  milk  plants. 

Another  avenue  thru  which  milk  is  infected  is  the  bottles.  Wher- 
ever there  is  complaint  from  the  consumer  concerning  ropy  milk, 
the  empty  bottles  are  certain  to  be  infected  with  the  ropy  milk  germs. 
Where  hand  washing  is  practiced  the  wash  water  is  not  hot  enough 
to  destroy  these  germs.  Accordingly  the  washing  vat  becomes  in- 
fected with  the  germs  mechanically  removed  from  the  bottles  and 
the  infection  passes  to  other  bottles  in  much  the  same  manner  as 
with  cans  washed  in  a  common  vat.  Unless  the  washed  bottles  are 
steamed  sufficiently  to  destroy  the  ropy  milk  germs  upon  them,  milk 
put  into  these  bottles  may  become  ropy  even  where  the  milk  has  been 
properly  pasteurized  and  otherwise  well  handled.  The  treatment  of 
the  bottles  with  steam,  if  short  as  in  the  mechanical  washers,  should 
bring  the  bottles  to  approximately  200°  F.,  but  this  temperature  may 
be  lower  if  the  period  of  heating  is  longer. 

RESULTS  OF  TREATMENT  AT  THE  BOTTLING  PLANT 

As  the  milk  company  was  operating  under  a  municipal  ordinance 
requiring  a  thoro  pasteurization  of  all  the  milk,  there  was  little  im- 


124  BULLETIN  No.  228 

provement  needed  in  the  pasteurizing  process  beyond  giving  close 
attention  to  the  details  of  handling  the  milk  at  the  beginning  and  at 
the  end  of  the  process.  The  difficulty  with  the  product  evidently 
arose  from  the  ropy  milk  germ  growing  in  the  milk  line  beyond  the 
pasteurizer.  Liberal  applications  of  steam  and  hot  water  to  the 
pipes,  tanks,  and  utensils  promptly  decreased  the  infection  to  the 
point  where  only  an  occasional  complaint  was  received  thru  the 
retail  department,  altho  careful  observations  showed  a  small  number 
of  ropy  milk  germs  in  some  of  the  bottled  milk.  A  routine  treatment 
of  all  the  milk  line  and  the  utensils  coming  into  contact  with  the 
milk  was  then  established,  and  apparently  the  trouble  disappeared. 
With  the  passing  of  the  emergency,  the  methods  of  handling  the 
plant  tended  to  revert  toward  the  earlier  routine,  and  after  a  few 
weeks  complaints  of  ropy  milk  again  came  from  the  consumers.  The 
prompt  reestablishment  of  a  thoro  steaming  of  all  portions  of  the 
milk  line  and  utensils,  special  attention  being  given  to  the  milk 
pumps,  was  followed  by  an  immediate  disappearance  of  the  trouble 
in  the  bottled  milk. 

OBSERVATIONS  IN  OTHER  MILK  PLANTS 

Since  ropy  milk  is  coming  to  be  a  frequent  experience  in  the 
routine  of  the  milk  business,  a  number  of  additional  opportunities 
have  presented  themselves  for  observing  similar  outbreaks  in  con- 
nection with  other  milk  plants.  These  observations  agree  in  empha- 
sizing two  points: 

(1)  An  outbreak  of  ropy  milk  which  is  creating  dissatisfaction 
on  the  part  of  the  milk  consumers  can  be  immediately  reduced  to  a 
level  where  it  will  cease  to  be  the  occasion  of  complaints  when  atten- 
tion is  given  to  proper  pasteurization  and  where  the  milk  is  protected 
from  the  introduction  of  the  ropy  milk  germs  between  the  pasteurizer 
and  the  bottle. 

(2)  When  the  milk  plant  has  been  thoroly  inoculated,  particu- 
larly if  the  milk  producers  continue  to  furnish  the  germs  with  the 
milk  supply,  the  final  and  complete  removal  of  the  last  traces  of  the 
ropy  milk  organisms  is  quite  difficult  and  likely  to  be  a  time-consum- 
ing process. 

CONCLUSIONS 

The  conclusions  will  be  found  embodied  in  the  Summary  at  the 
front  of  the  bulletin. 


UNIVERSITY  OF  ILLINOIS-URBANA 


